u-boot.inc: allow variable make targets

* Later versions of u-boot sometimes have top level make targets
  such as u-boot.imx, u-boot.kwb, and for upcoming TI devices
  u-boot.ti.
* These targets define different calls to the mkimage tool to
  change the images created, such as changing the load address.
* This change allows recipes to change the default make target
  of "all" to something like u-boot.ti or u-boot.imx by setting
  the UBOOT_MAKE_TARGET variable.

Signed-off-by: Chase Maupin <Chase.Maupin@ti.com>
Signed-off-by: Koen Kooi <koen@dominion.thruhere.net>

recipes-bsp/u-boot/u-boot.inc

@@ -18,6 +18,7 @@ UBOOT_MACHINE ?= "${MACHINE}_config"
 UBOOT_BINARY ?= "u-boot.bin"
 UBOOT_IMAGE ?= "u-boot-${MACHINE}-${PV}-${PR}.bin"
 UBOOT_SYMLINK ?= "u-boot-${MACHINE}.bin"
+UBOOT_MAKE_TARGET ?= "all"
 
 do_configure () {
 	oe_runmake ${UBOOT_MACHINE}
@@ -27,7 +28,7 @@ do_compile () {
 	unset LDFLAGS
 	unset CFLAGS
 	unset CPPFLAGS
-	oe_runmake all
+	oe_runmake ${UBOOT_MAKE_TARGET}
 	oe_runmake tools env
 }